Lung Cancer Screening with Low-Dose CT Scan May Lead to Overdiagnosis

Screening for lung cancer with low-dose CT scan may lead to overdiagnosis, according to the results of a study published in JAMA Internal Medicine.

Lung cancer is the leading cause of cancer death among both men and women in the United States. The disease is often detected at an advanced, difficult-to-treat stage.

Cancer screening involves the use of tests to detect cancer at an early stage in people who don’t have any symptoms of the disease. For cancers such as breast cancer, colorectal cancer, and cervical cancer, screening has contributed to decreased rates of cancer death. However, early detection of lung cancer has proven more difficult. In order for new screening methods to be adopted into routine clinical care, the measures must identify cancer early enough to improve outcomes, must be economically feasible, and must detect cancer with an acceptable degree of accuracy.

Low-dose CT scans are a special type of imaging scan that can identify smaller nodules than chest x-rays, making them a strong candidate for lung cancer screening. Although low-dose CT scans can detect lung cancer early, they also can detect indolent tumors that otherwise may not cause clinical symtpoms—leading to false-positive results and overdiagnosis. Overdiagnosis can be problematic on many levels—it leads to increased medical costs, anxiety, and unnecessary invasive procedures that can have deadly complications.

Researchers used data from the National Lung Screening Trial (NLST) in order to estimate overdiagnosis. The NLST was a randomized trial that compared two different screening techniques—low-dose computed tomography (LDCT) and chest radiography (CXR)—among 53,452 people at high risk for lung cancer. The participants were observed for 6.4 years in order to estimate the rate of overdiagnosis.

In the NLST, screening with LDCT showed a 20 percent relative reduction in mortality, and 320 participants were needed to screen in order to prevent one lung cancer death. However, despite the promise of this screening technique, there are risks as well. The current study found that the probability that any lung cancer detected by screening with LDCT was an overdiagnosis was 18.5 percent. What’s more, the probability that a non-small cell lung cancer (NSCLC) detected by LDCT was an overdiagnosis was 22.5 percent and the probability that a bronchioalveolar lung cancer detected by LDCT was an overdiagnosis was 78.9 percent. The number of cases of overdiagnosis found among the 320 participants who would need to be screened in the NLST to prevent 1 death from lung cancer was 1.38.

The researchers concluded that more than 18 percent of all lung cancers detected by LDCT in the NLST appear to be indolent. They state that overdiagnosis should be considered as one of the risks of LDCT screening for lung cancer.